1. Field of the Invention
The present invention relates to a thin film transistor, and more particularly to a method of manufacturing a thin film transistor using an organic semiconductor material as an active layer, a thin film transistor manufactured by the method, and a display device employing the same.
2. Description of the Related Art
A display device such as an organic light emitting display and a liquid crystal display which are small in thickness and operate with low voltages, unlike a cathode ray tube (CRT) which is bulky and operates with high voltages, is being widely used as the next generation display device.
Particularly, the organic light emitting display is a self-emitting display device in which electrons and holes injected into organic material through an anode and a cathode are recombined to generate excitons and light with a certain wavelength is emitted by energy of the generated excitons. Accordingly, the organic light emitting display is being highlighted as the next generation display device since it does not require a separate light source such as a backlight, and thus is low in its power consumption, as compared to the liquid crystal display, and in addition, may secure a wide viewing angle and a high response speed easily.
The organic light emitting display, which may be divided into a passive matrix type and an active matrix type depending on a driving method, has mainly employed the active matrix type in recent years owing to its low power consumption, high precision, high response speed, wide viewing angle and small thickness.
In such an active matrix type organic light emitting display, pixels as the basic unit for image representation are arranged in the form of a matrix, and a thin film transistor (TFT) is arranged as a switching element for each of the pixels to be controlled separately.
In recent years, with the wide spread of notebook computers, small portable terminals and so on, a flexible organic light emitting display has been developed, which uses flexible material adapted to such devices, such as plastic, which has little risk of breakage since it is lighter than glass and has flexibility, as substrate material.
It is advantageous for such a flexible organic light emitting display to use an organic TFT (OTFT), as the switching element, using organic semiconductor material, instead of a typical TFT using silicon as an active layer, because the organic semiconductor material allows a low-temperature process and secures flexibility.
Typically, the OTFT has a structure where a gate electrode and an active layer made of organic semiconductor material are formed on a substrate, with a gate insulating film disposed therebetween, and a source electrode and a drain electrode contact the active layer and are isolated from each other in correspondence to either side of the gate electrode.
In addition, the OTFT may be divided into a low molecule OTFT made of such materials as pentacene and a high molecule OTFT made of such as polythiophene depending on the organic semiconductor material composing the active layer.
The organic semiconductor material such as pentacene and polythiophene is difficult and complicated to be patterned since it has poor chemical and optical stability.
In addition, even after being patterned, such organic semiconductor material has difficulty in securing good pattern precision, leading to high possibility of occurrence of particles, which may result in cross-talk with adjacent OTFTs.